This invention relates to traffic data collection and intelligent routing systems for highway vehicles and, in particular, to a system and method for remotely collecting real-time traffic data and providing traffic forecasts and travel guidance for drivers of vehicles equipped to utilize the system.
Modern automobile travel is plagued by excessive traffic congestion due to continuously increasing automobile use. Drivers constantly seek optimum travel routes to minimize driving time. Local area radio and television stations transmit traffic alerts to inform drivers of blocked or congested traffic routes so that drivers familiar with alternate routes to their respective destinations can alter their planned route to minimize driving time. This, however, is often unproductive and results in increased travel time. Such traffic alerts disadvantageously require real-time reception by drivers prior to entering a congested traffic area. Traffic alerts are often missed because drivers are not tuned to the right station at the proper time. Besides, drivers tend to learn and routinely follow the same route day after day without becoming familiar with alternate routes even when they encounter heavy recurring congestion.
Roadside signs are also used to warn drivers and re-direct traffic during road construction or traffic congestion. For example, detour signs and electronic roadside billboards are used to suggest or require alternate routes. Some electronic billboards are located on main traffic arteries, warning of a pending traffic blockage or congestion. However, signs and billboards are usually too near the point of congestion or blockage to enable meaningful re-evaluation of a planned route, primarily because of the required close proximal relationship between the location of the sign and the point of congestion or blockage. There exists a continuing need to improve the collection of accurate traffic congestion data in order to provide accurate route planning information.
Governmental agencies provide emergency care service in response to roadside vehicle accidents, as is well known. Governmental agencies in North America have adopted the well-known xe2x80x9c911xe2x80x9d emergency call system through which road accidents are reported to enable emergency care services including police, fire and paramedic services to respond. The 911 emergency system relies on the reporting of accidents by private citizens who are typically either witnesses to an accident or are involved in the accident. However, when victims are incapacitated by injury, or when witnesses are unable to quickly locate a telephone, the 911 system fails. Moreover, critical time is often lost while searching for a telephone to place the 911 call. In addition, misinformation may be inadvertently given by victims or witnesses unfamiliar with the location of an accident, thereby directing the emergency care providers to a wrong location. There therefore exists a need for a system to more expeditiously provide accurate vehicle traffic accident information to emergency care providers.
Automobiles have also been equipped with experimental local area road-map systems which display a portion of a map of interest but do not use a global positioning system (GPS) to determine a vehicle position on the map. The driver is enabled to locate departure and destination points on the map, and then visually refers to the displayed map to see the current position of the vehicle as the driver travels toward the destination point. The map system displays a cursor to indicate the current position of a moving vehicle on the display map. The portion of the map that is displayed is periodically adjusted to keep the current position cursor in the center of the displayed map. The system uses a compass and a wheel sensor odometer to determine the current position as the vehicle travels on the road. The use of this map display system requires the driver to repetitively study the map and then mentally determine and select travel routes, directing attention away from the safe operation of the vehicle. This does not promote safe vehicle operation. Besides, the compass and wheel odometer technology causes map position error drifts, requiring re-calibration after travelling only a few miles. Moreover, the use of such a map system disadvantageously requires the entry of the departure point each time the driver begins a new route. Additionally, this map system does not perform route guidance and is not dynamically updated with current traffic information. There therefore exists a need to improve map systems with a driver friendly interface which reduces diversion away from the safe operation of the vehicle.
Certain experimental integrated dynamic vehicle guidance systems have been proposed. For example, Motorola has disclosed an intelligent vehicle highway system in block diagram form in a 1993 brochure, and DELCO Electronics has disclosed another intelligent vehicle highway system, also in block diagram form, in Automotive News published on Apr. 12, 1993. These systems use compass technology for vehicle positioning. However, displacement wheel sensors are plagued by tire slippage, tire wear and are relatively inaccurate, requiring re-calibration of a current vehicle position. Compasses suffer from drift, particularly when driving on a straight road for an extended period of time. These intelligent vehicle highway systems appear to use GPS satellite reception to enhance vehicle tracking on road-maps as part of a guidance and control system. GPS data is used to determine when drift errors become excessive and to indicate that re-calibration is necessary. However, the GPS data is not used for automatic re-calibration of a current vehicle position. These intelligent vehicle highway systems also use RF receivers to receive dynamic road condition information for dynamic route guidance, and contemplate infrastructure traffic monitoring, for example, a network of road magnetic sensing loops, and contemplate the RF broadcasting of dynamic traffic conditions for route guidance. The disclosed two-way RF communication through the use of a transceiver suggests a dedicated two-way RF radio data system. While two-way RF communication is possible, the flow of information between the vehicles and central systems appears to be exceedingly lopsided. It appears that the amount of the broadcast dynamic traffic flow information from a central traffic radio data control system to the vehicles would be far greater than the information transmitted from the vehicles to the central traffic control center, since the system is only used to report roadside incidents or accident emergency messages to the control center.
To overcome the above disadvantages, U.S. Pat. No. 5,504,482 entitled AUTOMOBILE NAVIGATION GUIDANCE, CONTROL AND SAFETY SYSTEM, which issued to K. D. Schreder on Apr. 2, 1996, discloses an automobile route guidance system. In this system, an automobile is equipped with an inertial measuring unit and GPS satellite navigational unit and a local area digitized street map system for precise electronic positioning and route guidance between departures and arrivals. The system is equipped with RF receivers to monitor updated traffic condition information for dynamic re-routing guidance to reduce travel time. It is also equipped with vehicle superseding controls activated during unstable vehicle conditions sensed by the inertial measuring unit to improve the safe operation of the automobile. Telecommunications equipment automatically notifies emergency care providers of the precise location of the automobile in the case of an accident so as to improve the response time of roadside emergency care providers.
Nevertheless, Schreder fails to address how the traffic data is collected for broadcasting road traffic conditions on which the system relies to provide the navigational guidance. A map-matching smoothing process disclosed by Schreder is also not optimal because it adjusts the display output so that a vehicle is displayed on a road rather than elsewhere on the map when navigation positioning errors occur. The process does the adjustment in a manner in which the cursor representing the current position of the vehicle is simply moved to the nearest available road position on the map. This may position the vehicle on a wrong road, particularly if more than one road is about equally near the cursor.
There are several known methods for collecting traffic data. In the most common, different sensing systems are used to collect traffic volume and vehicle speed. Sensors for counting purposes are installed along highways to measure traffic volume. Video cameras, color machine vision technology and pulsed laser range imaging technology are used to generate advanced traffic parameters such as driving speed and travel time. These technologies are disclosed, for example, in U.S. Pat. No. 5,546,188 entitled INTELLIGENT VEHICLE HIGHWAY SYSTEM SENSOR AND METHOD, which issued to Wangler et al. on Aug. 13, 1996. In other applications, multifunctional roadway reference systems are suggested, in which discrete marks installed in the center of a traffic lane code one or more bits of information, such as geographical position, upcoming road geometry and the like. An example of roadway reference systems is disclosed in U.S. Pat. No. 5,347,456 which is entitled INTELLIGENT ROADWAY REFERENCE SYSTEM FOR VEHICLE LATERAL GUIDANCE AND CONTROL. This patent issued to Zhang et al. on Sep. 13, 1994.
Given the size of a continental highway system, using sensors and/or cameras to collect road traffic data for each and every public road on the continent is impractical. Considering the technical considerations and the system costs, a method for collecting dynamic traffic data using equipment installed in vehicles is required. Furthermore, the prior art does not teach a general road network traffic forecast system for broadcasting road traffic forecasts to enable drivers to plan a trip in advance. There exists a need for improved remote road traffic data collection and traffic forecast system.
An object of the invention is to provide a remote traffic data collection and intelligent vehicle route planning system.
Another object of the invention is to provide a road network traffic forecasting system.
Yet another object of the invention is to provide drivers of automobiles with a route planning system.
Yet another object of the invention is to provide a route planning system which uses GPS information to accurately position a vehicle within a digitized road network.
Still another object of the invention is to provide a route planning system which computes optimal routes between a departure and a destination point based on road traffic forecasts and current road condition information.
A further object of the invention is to provide an economical system for remote collection of road traffic data from a wide area to enable road traffic forecasts.
Yet a further object of the invention is to provide a system which disseminates road traffic forecast information to travelling vehicles and collects road traffic data at a traffic service center.
In general terms, a remote traffic data collection and intelligent vehicle highway system comprises a road traffic data collection sub-system, a communication sub-system, a traffic service center that stores and processes road traffic information and provides real-time road traffic forecasts for drivers, and a route guidance sub-system. The road traffic data collection sub-system and the route guidance sub-system are incorporated in in-vehicle equipment. The road traffic data collection sub-system uses global positioning information received from a global position system (GPS) by the in-vehicle equipment which uses the information to compute a position of the vehicle on a digitized road network. The digitized road network includes nodes substantially representing road-intersections, and straight links representing road segments and indicating traffic directions between the nodes. A radio-frequency communication system transmits the vehicle position data to the traffic service center which processes the data for use in the road traffic forecasts. The vehicle position data transmitted includes only data related to the nodes. The road traffic forecasts are based on data collected over a period of weeks. The road traffic data collected at a given time on a given day of a week for a specific road segment is processed so that an average travel time or speed for the road segment at the given time on the given day of the week is determined and is used to forecast the travel time or speed in normal road conditions for the road segment at the same time on the same day in the future.
Road traffic speed and volume varies with time of day and day of week. However, under normal conditions that are not affected by an abnormal situation, such as a traffic accident, road construction, bad weather, holidays or public activities, the traffic speed and volume for one day of a week is similar to that of the same day of other weeks. This fact provides a basis for road traffic forecasting under normal conditions. The road traffic forecasting is improved if factors associated with specific abnormal conditions that occur at a time a forecast is made are used to adjust projected travel times.
A method of accurately locating a vehicle on a digitized road network that is formed of nodes and links between the nodes is also described. The method includes the steps of obtaining a geographical position of a vehicle and moving the geographical position to a nearest link in accordance with information associated with a node which the vehicle last passed, in order to avoid locating the vehicle on a wrong link on the digitized road network.
In specific terms, in accordance with one aspect of the invention, there is provided a method for forecasting road traffic comprising the steps of:
(a) periodically collecting vehicle position data at a traffic service center, the vehicle position data being dynamically reported by equipped vehicles travelling roads in a given area, the equipped vehicles being adapted to receive geographical position data into relative vehicle position data to determine a position of the vehicle with respect to a digitized road network of nodes interconnected by straight links, the links indicating traffic directions between the nodes, the vehicle position data reported including only data related to the nodes, the geographical position data being received and converted into a relative position on the digitized road network at a predetermined collection interval (CI) and the vehicle position data being reported at a predetermined reporting interval (RI), wherein RI greater than CI;
(b) computing real travel time of vehicles travelling the links using the vehicle position data;
(c) determining a set of real travel time samples for a link L i from actual travel times of vehicles that travelled the link during a given time interval starting at or including a time t on a given day D of a week; and
(d) calculating an average travel time T1 for the link L1 using the set of travel time samples at a time t on the day D, and storing the average travel time T1 for use in predicting a travel time for the link L1.
Preferably, the method further comprises steps of repeating steps of (c) and (d) to calculate an average travel time T2 for a link L2 at a time (t+T1), an average travel time T3 for a link L3 at a time (t+T1+T2), up to an average travel time Tn for a link Ln at a time (t+T1+T2+. . . +Tnxe2x88x921); calculating an average travel time TR of a route R including continuous links L1, L2, L3, . . . and Ln at the departure time t by summing up the average travel times T1, T2, T3, . . . and Tn for predicting a travel time for route R at the departure time t on the day D.
If the route R further includes some critical left-turns where waiting times cannot be ignored, then left-turn time is also added to the travel time for route R in the same way as described above.
In accordance with another aspect of the invention, there is provided a remote traffic data collection and intelligent routing system for highway vehicles, comprising:
a traffic service center adapted to receive and process vehicle position data to determine an average travel time or travel speed for any specific link during a given forecast interval on a given day of the a week, and broadcast a digitized road network consisting of nodes interconnected by straight links representing road segments, the links indicating traffic direction between the nodes, and to concurrently, or independently broadcast a forecast of an average travel time or travel speed for the specific link during the given forecast interval on the given day in the future;
a remote traffic data collection sub-system including in-vehicle devices in a plurality of vehicles, each of the devices being adapted to receive, from time to time, global positioning information from a Global Positioning System (GPS) and to convert the global positioning information into the vehicle position data associated with at least some of the nodes on the digitized road network, the global positioning information being received and converted into the vehicle position data at a predetermined collection interval (CI); and
a communication sub-system in each device and the traffic service center for communicating the vehicle position data from the vehicle to the traffic service center, and the digitized load network and the road traffic forecast from the traffic service center to the vehicle, the vehicle position data being reported to the traffic service center at a predetermined reporting interval (RI), wherein RI greater than CI.
The system provides a practical and economic solution for providing an intelligent vehicle highway system serving a wide area and providing reliable traffic forecasts for vehicles equipped with the system.